The present disclosure relates generally to setting pre-congestion notification (PCN) admission and preemption thresholds in computer networks.
The IETF (Internet Engineering Task Force) has proposed methods for measurement based admission control and preemption techniques. (See e.g., B. Briscoe et al., “A Framework for Admission Control over DiffServ using Pre-Congestion Notification”, IETF draft-briscoe-tsvwg-cl-architecture-03.txt, Jun. 26, 2006, B. Briscoe et al., “Pre-Congestion Notification Marking”, IETF draft-briscoe-tsvwg-cl-phb-02.txt, Jun. 26, 2006, and P. Eardley, “Pre-Congestion Notification Architecture”, IETF draft-eardley-pcn-architecture-00, Jun. 20, 2007, which are incorporated by reference herein in their entirety). The method relies on core nodes providing explicit notification information to edge nodes when the traffic load on a core link reaches certain levels. The edge nodes use some of this explicit notification information to decide whether new calls should be accepted. This is referred to as a flow “Admission” process. The edge nodes may also use some explicit notification information to drop calls that are already in place if needed. This is referred to as a flow “Preemption” (also known as “termination”) process. In order to provide the explicit notification information, the core node meters voice traffic load on each link, and when it reaches predefined thresholds the core node sets particular bits in the header of packets (PCN-bits).
An important requirement for the admission control and preemption technique described above is that the admission and preemption processes are able to react at different load thresholds. The current approach thus uses two separate thresholds; one for limiting admission of new flows under normal circumstances, and one for preempting traffic if unexpected conditions such as network failures or sudden changes in traffic matrix occur.
The proposed methods for admission control and preemption described above do not address how to set the thresholds used in congestion and pre-congestion notification.